The present invention relates to an idle speed control apparatus and method for an internal combustion engine which controls the rotational speed or the number of revolutions per minute of the engine during idling.
There have been known many internal combustion engines for a vehicle equipped with an idle speed control apparatus which senses the engine load and controls, under the action of an actuator having a relatively high response characteristic, the amount of intake air sucked into the engine at an appropriate level in accordance with the engine load as sensed so as to prevent a sudden change in the rotational speed or the number of revolutions per minute of the engine and stabilize the engine rotation. A typical example of such a high-response actuator is a linear solenoid which is able to control the amount of intake air in accordance with the magnitude of current supplied thereto. Another example is a duty solenoid in which a solenoid is periodically turned on and off with a prescribed cycle so as to regulate the duty ratio thereof whereby the amount of intake air sucked into the engine is properly controlled.
In operation of the above-described idle speed control apparatuses, during stable operations of the engine in which the engine load is substantially constant or gradually changing as when the engine is idling or operating under a constant load such as when an air conditioner is on, when a shift lever for an automatic transmission (hereinafter simply referred to as A/T) for the engine is in a drive range (hereinafter simply referred to as a D range) and the like, the amount of intake air sucked into the engine is calculated uniquely depending on the load conditions of the engine. On the other hand, during transient or rapidly changing conditions of the engine in which the engine load is rapidly changing as when an air conditioner is being turned on or off, the amount of intake air is controlled such that the target level for air intake is changed from a first value for the off-condition of the air conditioner into a second value for the on-condition thereof.
With the above-described known idle speed control apparatuses, however, at the time when the engine load is changing as when the air conditioner is being turned on or off, when an automatic transmission is being changed from the neutral range into the drive range, or the like, sometimes there arises a situation in which the load condition of the engine as sensed by a load sensor does not match the actual load on the engine due, for example, to a mechanical delay in the transmission of the operation from the air conditioner to the engine, due to a hydraulic delay in the transmission of the oil pressure in the automatic transmission.
Accordingly, in this state of mismatching between the actual and the sensed engine load, when the amount of intake air is changed from a first value suited to the inoperative condition of the air conditioner into a second value suited to the operative condition thereof or vice versa, the response of the actuator for controlling the amount of intake air is relatively quick so that the amount of intake air to be sucked into the engine instantaneously becomes too great or too small, resulting in an instantaneous increase or decrease in the idle number of revolutions per minute of the engine. This sometimes leads to an impairment in the driving sensation of the driver.